iPadOS15 is still a beta release. When you enrolled in the Apple Beta Programme you will have accepted the likelihood of experiencing bugs and unresolved software issues - and will have similarly accepted that participation within the beta programme is without technical support.
The Terms of Use that govern participation within these Support Communities precludes discussion of beta software. Guidance here is limited to restoring the current production version of iPadOS.
If you are currently enrolled in a beta programme and wish to return to using the current production version, this support page provides the necessary information to remove the beta from your iPad:
How to uninstall iOS beta software - Apple Support